www. b elling .com . cn 1 1 . 5 a 1.5mhz synchronous buck converter b l8027 description the BL8027 is a high - efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture . the device is available in an adjustable version. supply current with no load is 40ua and drops to < 1ua in shutdown. the 2.5v to 6v input voltage range makes the BL8027 ideally suited for single li - ion battery powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. pwm/pfm mode operation provides very low output ripple voltage for noise sensitive applications. switching frequency is internally set at 1.5mhz, allowing the use of small surface mount inductors and capacitors. low output voltages are easily supported with the 0.6v feedback reference v oltage. the BL8027 is available in sot23 - 5 package. features ? high efficiency: up to 96% ? 2.5v to 6v input voltage range ? 1.5 mhz constant frequency operation ? no schottky diode required ? low dropout operation:100% duty cycle ? pfm mode for high efficiency in light load ? over temperature protected ? low quiescent current: 40a ? short circuit protection ? inrush current limit and soft start ? available in sot23 - 5 applications ? cellular and smart phones ? wireless and dsl modems ? pdas ? portable instruments ? digital still and video cameras ? pc cards typical application pin out & marking kb : product code yw : date code ( year & week) note: c in and c out recommended using ceramic capacitors. if the electrolytic capacitor is used, a capacitor of smaller esr value needs to be selected. bl8 02 7 l c 2 1 3 8 l 2 . 2 h c o u t 1 0 f c 1 2 2 p f o p t . r 1 2 0 0 k 1 % r 2 1 0 0 k 1 % c i n 1 0 f v i n s w e n f b g n d v i n v o u t 1 2 3 5 4 s o t 2 3 - 5 v i n s w f b e n g n d k b y w
www. b elling .com .cn 2 b l8027 ordering information part no. package tape&reel BL8027 c b5 tr sot23 - 5 3000/reel absolute maximum rating parameter value max input voltage 8 v max voltage all pins 8v max operating junction temperature(tj) 1 25 ? c ambient temperature(ta) - 4 0 ? c C 85 ? c maximum power dissipation sot23 - 5 400m w storage temperature(ts) - 40 ? c - 150 ? c lead temperature & time 260 ? c , 10s note: exceed these limits to damage to the device. exposure to absolute maximum rating conditions may affect device reliability. electrical characteristics ( v in = v en =3.6 v, t a =25 ? c ) symbol parameter conditions min typ max unit v in input voltage range 2.5 6 v vref feedback voltage 0. 58 8 0. 6 0.61 2 v iq quiescent current v fb = vref* 90%, vin=5.0v, iload=0ma 15 0 3 00 ua v fb = vref* 105%, vin=5.0v, iload=0ma 40 70 ua v en = 0v, v in =4.2v 0.1 1.0 ua lnreg line regulation vin=2.5 v to 6 v 0.1 0.2 %/v ldreg load regulation 0.5 % fsoc switching frequency 1.5 mhz rdsonp pmos rdson i sw =100ma 300 mohm rdsonn nmos rdson i sw = - 100ma 200 mohm ilimit peak current limit vin=5 v , vout=3.3v 2.2 a inoload* vin=5v, vout=3.3v, iout=0 43 ua iswlk sw leakage current v en =0v,v in =v sw =5v 1 ua ienlk en leakage current 1 ua vh_en en input high voltage 1 .04 v vl_en en input low voltage 0.98 v note: * when dutycycle > 9 0 %, inoload will increase. e .g . vin=3. 5 v/vout=3.3v, inoload= 800u a. pin description pin # name description 1 en chip enable pin. drive en above 1.5v to turn on the part. drive en below 0. 3 v to turn it off. do not leave en floating. 2 gnd ground 3 sw power switch output. it is the switch node connection to inductor. this pin connects to the drains of the internal p - ch and n - ch mosfet switches. 4 v in supply voltage. must be closely decoupled to gnd with a 10 f or greater ceramic capacitor. 5 fb output voltage feedback pin. an internal resistive divider divides the output voltage down for comparison to the internal reference voltage.
www. b elling .com .cn 3 b l8027 electrical performance tested under ta=25 ? c , unless otherwise specified output ripple and sw at 1 .5 a load vin=5v / vout= 3.3 v ch1 l 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.001 0.01 0.1 1 10 efficiency iout (a) efficiency vs. output current (vout=1.2v) vin=2.5v vin=3.0v vin=4.0v vin=5.0v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.001 0.01 0.1 1 10 efficiency iout (a) efficiency vs. output current (vout=1.8v) vin=3.0v vin=3.6v vin=5.0v vin=6.0v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.001 0.01 0.1 1 10 efficiency iout (a) efficiency vs. output current (vout=3.3v) vin=3.8v vin=4.0v vin=5.0v vin=6.0v
www. b elling .com .cn 4 b l8027 block diagram detailed description the BL8027 uses a constant frequency, current mode step - down architecture. both the main (p - channel mosfet) and synchronous (n - channel mosfet) switches are internal. during normal operation, the internal top power mosfet is turned on each cycle when the oscillator sets the rs latch, and turned off when the current comparator, icomp, resets the rs latch. the peak inductor current at which icomp resets the rs latch, is controlled by the output of error amplifier ea. when the load current increases, it causes a slight decrease in the feedback voltage, fb, relative to the 0.6v reference, which in turn, causes the ea amplifiers output voltage to increase until th e average inductor current matches the new load current. while the top mosfet is off, the bottom mosfet is turned on until either the inductor current starts to reverse, as indicated by the current reversal comparator ircmp, or the beginning of the next cl ock cycle. applications information setting the output voltage in the adjustable version, the output voltage is set by a resistive divider according to the following formula: the external resistive divider is connected to the output, allowing remote voltage sensing as shown in on page 1 . inductor selection for most designs, the BL8027 operates with inductors of 1h to 4.7h. low inductance values are physically smaller but require faster switchin g, which results in some efficiency loss. the inductor value can be derived from the following equation: where is inductor ripple current. large value inductors result in lower ripple current and small value inductors result in high ripple current. for optimum voltage - positioning load transients, choose an inductor with dc series resistance in the 50m? to 150m? ra nge. 1 / 1 2 ? ? fb out v v r r ? ? osc l in out in out f i v v v v l ? ? ? ? ? ? l i ?
www. b elling .com .cn 5 b l8027 input capacitor selection higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. their high ripple current, high voltage rating and low esr make them ideal for switching regulator applications. because the BL8027 s control loop does not depend on the output capacitors esr for stable operation, ceramic capacitors can be used freely to achieve very low output ripple and small circuit size. however, care must be taken when ceramic capacitors are used at the input and the output. when a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, vin. at best, this ringing can couple to the output and be mistaken as loop instability. at worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at vin, large enough to damage the part. when choosing the input and output ceramic capacitors, choose the x5r or x7r dielectric formulation s. these dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. pc board layout checklist when laying out the printed circuit board, the following checking should be used to ensure proper operation of the BL8027 . check the following in your layout: 1) the power traces, consisting of the gnd trace, the sw trace and the vin trace should be kept sho rt, direct and wide. 2) does the (+) plates of cin connect to vin as closely as possible? this capacitor provides the ac current to the internal power mosfets. 3) keep the switching node, sw, away from the sensitive vout node. 4) keep the ( - ) plates of cin and cout as close as possible package out line package sot23 - 5 devices per reel 3000 unit mm package specification
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